SVBONY SV188P 2in Dielectric Mirror Star Diagonal - High Reflectivity

In this review the SVBONY SV188P 2in dielectric mirror star diagonal is evaluated for amateur and intermediate telescope users who want brighter, cleaner views and a comfortable 90 degree eyepiece angle. The single biggest reason to consider this diagonal is its dielectric coating with up to 99% reflectivity, which preserves light and contrast compared with enhanced aluminum alternatives. The diagonal ships with a 2in to 1.25in converter, uses a brass compression ring and an eyepiece anti-contact block to protect optics, and is finished internally to reduce stray light for clearer images.

Key Features

• High-reflective dielectric coating: Delivers up to 99% reflectivity for improved brightness and contrast across the field of view.
• 2in format with 1.25in adapter: Accepts 2in eyepieces and filters while including a converter for 1.25in eyepiece compatibility.
• Durable mechanical design: Aluminum alloy body with black bright oxidation finish provides a solid, attractive housing for field use.
• Eyepiece protection system: Side screw locking with a brass pressure ring and anti-contact block reduces risk of scratching eyepiece barrels.
• Interior stray light control: Matte paint and a velvet-lined burgundy cover minimize internal reflections for a cleaner image.
• 90 degree viewing and upright image: Provides a comfortable observing angle and upright orientation that reduces the need for post-image processing.

Who It's For

The SV188P is a good choice for backyard observers using 2in focusers or larger refractors who value maximum light transfer and straightforward mechanical protection for their eyepieces. Users who frequently switch between 2in and 1.25in eyepieces will appreciate the included converter and the ability to fit 2in filters.

Those who need extreme color-critical imaging or who require mirror diagonals for specialized instrumentation should compare options; a few customers reported mixed results on color accuracy. Observers with only 1.25in focusers who never use 2in accessories may find the larger format unnecessary.

Pros & Cons

Pros

• Excellent light transfer and contrast from the dielectric mirror.
• Solid build with aluminum alloy body and an attractive black oxidation finish.
• Thoughtful eyepiece protection via a brass pressure ring and anti-contact block.
• Internal matte treatment effectively reduces stray light for clearer views.

Cons

• Some users noted mixed results with color accuracy compared with other diagonals.
• Large 2in format may be overkill for observers who only use 1.25in eyepieces.

Specifications

Format	2in diagonal with 2in to 1.25in converter
Reflective coating	High-reflective dielectric coating, up to 99% reflectivity
Mirror quality	High-precision plane mirror, 1/4 wavelength error
Body material	Aluminum alloy with black bright oxidation
Locking design	Side screw locking with brass pressure ring and anti-contact block
Stray light control	Matte interior paint and velvet-lined burgundy cover

Our Verdict

The SVBONY SV188P 2in dielectric mirror diagonal is a practical upgrade for observers who want brighter, higher-contrast views and a durable, eyepiece-friendly mechanical design. It represents good value for visual work, especially with larger refractors and when using 2in eyepieces or filters, though those prioritizing absolute color fidelity for imaging should compare alternatives.

Frequently Asked Questions

Will this fit 1.25in eyepieces?
Yes. The diagonal includes a 2in to 1.25in converter so it can accept 1.25in eyepieces and accessories.

Does the diagonal change the image orientation?
The diagonal provides an upright image for comfortable observation at a 90 degree angle; it is intended for visual observing, not for providing a mirrored or flipped output for imaging rigs.

How does it control stray light?
The interior is treated with matte paint and a velvet-lined burgundy cover to reduce internal reflections and improve contrast.